Fuel storage systems for vehicles include a fuel tank. The fuel tank includes an inlet, to which a filler pipe is attached, through which fuel is dispensed into the tank. The fuel tank further includes an outlet, through which fuel is directed to an engine. The fuel tank may further include a fuel vapor vent valve assembly, disposed on a top wall of the fuel tank. The fuel vapor vent valve assembly provides an outlet to vent fuel vapors from within an interior of the fuel tank.
During refueling of the fuel tank, operation of the vehicle, or as a result of temperature change of the fuel, the vapor pressure within the tank may change, i.e., increase or decrease. The fuel vapor vent valve assembly vents the fuel vapor from within the fuel tank to maintain a vapor head within a predetermined range when the vapor pressure rises above the predetermined range. The fuel vapor vent valve assembly may further include a liquid/vapor discriminator, commonly referred to as a roll-over valve. The liquid/vapor discriminator is configured to allow the fuel vapors to pass through the fuel vapor vent valve assembly during normal operating conditions, but is configured to block fluid communication between the fuel tank and the fuel vapor vent valve assembly when the fuel tank is oriented at an extreme angle or upside down, such as in the event of a vehicular roll-over. The fuel tank may further include a vacuum relief valve, which is configured to relieve a vacuum pressure from within the fuel tank.